Support for case sensitivity settings

Hi! As you probably know, there are 2 options for case sensitivity:

• Windows use case sensitive paths,
• other systems like macOS or Linux use case insensitive paths

I checked how memfs behave and it seems that it uses case sensitive approach:

const { fs } = require('memfs');

fs.writeFileSync('/my/Case/sensitive/Path.txt', 'content');

console.log(fs.readFileSync('/my/case/sensitive/path.txt'));
// logs undefined
// if I would use native fs on macOS or Linux, I would get "content" logged
// so it's kind of inconsistency between memfs and fs

It would be nice if:

1. there would be an option to configure it
2. the default behavior would be to use system settings